The present invention is related to cardiac ablation treatments.
Ablation therapies can be used to treat certain conditions of the heart including atrial fibrillation. Ablation therapies are typically administered to regions in the heart to kill tissue and form lesions in selected heart tissue such that the lesion formed by the ablated heart tissue is unable to support conduction, and hence, fibrillation.
Generally stated, during atrial fibrillation, propagation of the electrical excitation wavefront travels along the surface substrate tissue (wall). To be effective, the ablated tissue lesion should be transmural such that the tissue is destroyed along the surface and through the thickness of the substrate tissue (or the thickness of the wall) about the lesion (i.e., not merely a surface or superficial lesion). Typically, the ablation therapy is delivered so that a desired contiguous (conventionally linear) lesion pattern or length is formed in the selected myocardial tissue, which kills all viable excitable cells about the surface of the lesion and through the wall thickness underlying the lesion so that the heart is unable to maintain fibrillation. That is, the lesion electrically insulates and separates side-by-side adjacent segments in the atria so that the adjacent segments are effectively electrically isolated from each other by the lesion in a manner that inhibits electrical conduction between the adjacent segments.
In some applications, transvenous or intravenous ablation catheters having one or more electrodes can be inserted into one or more heart cavities to administer the ablation treatment to kill selected heart tissue. Unfortunately, in conventional ablation treatments, it can be difficult to assess when to terminate the administration of the treatment in a manner which identifies when sufficient tissue has been destroyed to provide a clinically efficacious (transmural) linear ablation lesion. Particularly, xe2x80x9cblindxe2x80x9d or catheter-based ablation of cardiac tissue (such as to treat atrial fibrillation) may be more effective when patient-specific valid endpoints are used to recognize when a clinically efficacious lesion has been created. In the early ablation experience, acute termination followed by non-inducibility of the arrhythmia were used. Because these endpoints correlated poorly with long-term success, however, other parameters were developed. Presently, it is believed that impedance and temperature measurements during the delivery of RF energy and the presence of conduction block after delivery of RF energy are the most common endpoints used in clinical practice.
The present invention provides methods, systems, and computer program products for assessing the condition of the lesion formed in cardiac tissue during myocardial ablation. The systems and methods and computer programs of the invention can be used to monitor the lesion site and identify when sufficient necrosis has occurred. Further, in certain embodiments, the administration of the selected cardiac ablation therapy can be controlled so as to automatically terminate the ablation treatment upon the determination that the lesion site is a clinically efficacious lesion during an ablation procedure. The term xe2x80x9cclinically efficaciousxe2x80x9d is meant to indicate that the lesion is able to substantially block myocardial propagation between adjacent tissue segments and, as such, includes the term xe2x80x9ctransmuralxe2x80x9d which means that the extent of necrosis is such that the substrate or tissue destroyed by the ablation procedure to create the lesion is contiguous about the surface of the lesion site and extends through the thickness of the wall to electrically isolate adjacent segments positioned on opposing sides of the lesion. The transmural nature of the lesiton site is also indicated when myocardial necrosis is sufficient to extend from the endocardial to the epicardial layer.
In certain embodiments, the methods and systems of the present invention can be used while a subject is experiencing fibrillation (typically atrial fibrillation). In other embodiments, the systems and methods can be used during normal sinus rhythm.
Certain embodiments of the present invention are directed to methods for controlling the administration of an ablation treatment to cardiac tissue of a patient experiencing (an onset of or a continued state of unstable or fibrillating state). The method can include the steps of: (a) measuring at least one electrophysiologic parameter of heart tissue proximate a targeted ablation treatment region while the patient is in atrial fibrillation; (b) ablating the targeted ablation treatment region to form a lesion in cardiac tissue; (c) measuring the at least one electrophysiologic parameter of cardiac tissue proximate the targeted ablation treatment region after the first measuring step and after the ablating step has been commenced while the patient is in atrial fibrillation; (d) comparing the at least one electrophysiologic parameter measured during steps (a) and (c) to determine whether the lesion formed by the ablating step is clinically efficacious.
In certain embodiments, methods for controlling the delivery of a selected ablation treatment to cardiac tissue can include the steps of: delivering a desired ablation therapy to the selected ablation treatment region to form a lesion in the cardiac tissue; obtaining first and second measurements of at least one electrophysiologic signal associated with cardiac tissue in the selected ablation treatment region from a plurality of different positions associated with the lesion, wherein the first measurements are obtained before the delivering step is initiated; and comparing the first and second measurements of the obtaining step to identify when sufficient tissue has been destroyed at the lesion so as to stop the ablation of the tissue of the delivering step.
In certain embodiments, the delivering step may be carried out by a multiple electrode RF ablation catheter, and the obtaining step can include sensing the electrical activity of the at least one electrophysiologic signal from a plurality of different electrical couplings of the multiple electrodes on the ablation catheter.
Still other embodiments are directed to methods for identifying when a lesion is clinically efficacious during delivery of a selected ablation therapy to form same. The methods can include: (a) measuring the standard deviation of electrogram amplitude of heart tissue proximate a targeted ablation treatment region while the patient is in atrial fibrillation; (b) ablating the targeted ablation treatment region to form a lesion in the heart tissue; (c) measuring the standard deviation of the electrogram amplitude of heart tissue proximate the targeted ablation treatment region after the first measuring step and after the ablating step has been commenced (during ablation or as the ablation is temporally halted) while the patient is in atrial fibrillation; (d) comparing the standard deviation measure of the electrogram amplitude measured during steps (a) and (c); and (e) determining whether the lesion formed by the ablating step is clinically efficacious based on the comparing step.
In some embodiments, the method can also include the step of measuring the ablation treatment temperature and time during the ablating step, and the determining step can further consider the temperature and time to assess whether the lesion is clinically efficacious (or transmural).
In certain embodiments, systems for ablating cardiac tissue can include an ablation source configured to expose targeted cardiac tissue to temperatures above about 45xc2x0 C. for a period of time to form a lesion in cardiac tissue. The system can also include a controller operably associated with the ablation source and a power source operably associated with the controller and the ablation source. The system can include a plurality of (sensing) electrodes operably associated with the controller and configured to be positioned, in operation, proximate the lesion site of the targeted cardiac tissue. In operation, the controller receives electrical signals corresponding to electrical activity of the cardiac tissue about the lesion from the electrodes before initiation of the thermal ablation therapy and at desired times during the ablation therapy treatment session. The controller analyzes the electrical signals to control the duration of the ablation treatment from the ablation source. The electrodes are configured to relay information to the controller about the electrical activity of the cardiac tissue about the lesion and to ablate the tissue at the lesion site.
In certain embodiments, the ablation source comprises a multiple electrode catheter configured to transmit RF energy to the cardiac tissue and the multiple electrodes can be configured such that, in operation, they can be electrically switched so as to be coupled in a plurality of different manners to sense and relay information to the controller about electrical activity over larger regions about the lesion.
In other embodiments, systems for ablating cardiac tissue can include an ablation source configured to expose targeted cardiac tissue to temperatures above about 45xc2x0 C. for a period of time to form a lesion in cardiac tissue and a controller operably associated with the ablation source. The system can also include a power source operably associated with the controller and the ablation source and at least one sensing electrode operably associated with the controller and configured, in operation, to be positioned proximate the lesion site of the targeted cardiac tissue. The controller is configured to receive electrical signals from the at least one sensing electrode before initiation of the thermal ablation therapy and at desired times during the ablation therapy treatment session. The electrical signals can be obtained during (atrial) fibrillation and can correspond to the measure of the standard deviation of the electrogram amplitude of the tissue during fibrillation. The controller (or computer programs or data processing systems associated therewith) is configured to analyze the standard deviation of the amplitude of the fibrillating tissue about the lesion to control the duration of the ablation treatment from the ablation source.
Other embodiments include computer program products for identifying whether an ablation lesion in cardiac tissue of a subject being treated for a cardiac condition is clinically efficacious during an ablation therapy session. The computer program product can include a computer readable storage medium having computer readable program code embodied in the medium. The computer-readable program code can include: (a) computer readable program code for identifying a first measurement of the electrical activity corresponding to the standard deviation of the amplitude of the electrogram in the cardiac tissue located about a lesion site while a subject is experiencing atrial fibrillation; (b) computer readable program code for identifying a second measurement of the electrical activity corresponding to the standard deviation of the amplitude of the electrogram in the cardiac tissue located about the lesion site after the lesion site has been exposed to at least a portion of a selected ablation therapy; and (c) computer readable program code for comparing the first and second measurements of the standard deviation of the amplitude of the electrogram activity to determine whether the lesion is clinically efficacious.
In certain embodiments the computer program product can include computer readable program code for assessing the amount of time, the ablation temperature, and the type of ablation therapy which the tissue proximate the lesion has been exposed and for considering this information in determining the efficacy of the treatment.
Another embodiment of the present invention, similar to the above, is directed to a computer program product for identifying whether an ablation lesion in cardiac tissue of a subject being treated for a cardiac condition is clinically efficacious during an ablation therapy session. The computer program product includes a computer readable storage medium having computer readable program code embodied in said medium. The computer-readable program code can include: (a) computer readable program code for receiving data corresponding to a first set of information regarding the electrical activity in the cardiac tissue from multiple regions about a lesion site prior to active initiation of the ablation therapy; (b) computer readable program code for receiving data corresponding to a second set of information regarding the electrical activity in the cardiac tissue from multiple regions about the lesion site after the lesion site has been exposed to at least a portion of a selected ablation therapy; and (c) computer readable program code for comparing the data from the first and second sets of information to determine whether the lesion is clinically efficacious about its perimeter.
In certain embodiments, the computer program product can include computer readable program code for acquiring and analyzing or xe2x80x9cscanningxe2x80x9d the lesion site to obtain a plurality of data sets over different spatial regions about the lesion site during the ablation therapy and computer readable program code for electrically changing the couplings of electrodes used to deliver the ablation therapy to electrical sense and relay information about the electrical activity of the lesion site from a plurality of different spatial perspectives during the ablation therapy session.
The foregoing and other objects and aspects of the present invention are explained in detail in the specification set forth below.